You can order them in bulk (10 or 25 packs) for $0.00; they deliver them to your door.
Local "Pack and Ship" stores often carry the full range of Small, Medium, and Large sizes. 💡 Pro-Tips for Your Story where to buy flat rate shipping boxes
Most USPS locations provide them for free in the lobby. You can order them in bulk (10 or 25 packs) for $0
Staples or OfficeDepot often stock them, though usually for a small markup or as part of a shipping service. Staples or OfficeDepot often stock them, though usually
Elias was a restorer of broken things—chipped porcelain dolls, rusted pocket watches, and weathered letters. His clients lived in distant corners of the world, connected only by the hope that their treasures would arrive intact. He chose the Flat Rate Box not for the price, but for the promise: "If it fits, it ships."